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baby steps toward fixing some problems with inbound GEPs that overflow, as discussed 2 months ago or so.

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Make sure we do not emit index computations with NSW flags so that we dont get an undef value if the GEP overflows

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160589 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nuno Lopes 2012-07-20 23:07:40 +00:00
parent 78435f6bb7
commit c606c3ff91
3 changed files with 16 additions and 3 deletions
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7
include/llvm/Transforms/Utils/Local.h
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@ -168,15 +168,18 @@ static inline unsigned getKnownAlignment(Value *V, const TargetData *TD = 0) {
/// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
/// code necessary to compute the offset from the base pointer (without adding
/// in the base pointer). Return the result as a signed integer of intptr size.
/// When NoAssumptions is true, no assumptions about index computation not
/// overflowing is made.
template<typename IRBuilderTy>
Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP) {
Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP,
bool NoAssumptions = false) {
gep_type_iterator GTI = gep_type_begin(GEP);
Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
Value *Result = Constant::getNullValue(IntPtrTy);
// If the GEP is inbounds, we know that none of the addressing operations will
// overflow in an unsigned sense.
bool isInBounds = cast<GEPOperator>(GEP)->isInBounds();
bool isInBounds = cast<GEPOperator>(GEP)->isInBounds() && !NoAssumptions;
// Build a mask for high order bits.
unsigned IntPtrWidth = TD.getPointerSizeInBits();

2
lib/Analysis/MemoryBuiltins.cpp
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@ -645,7 +645,7 @@ ObjectSizeOffsetEvaluator::visitGEPOperator(GEPOperator &GEP) {
if (!bothKnown(PtrData))
return unknown();
Value *Offset = EmitGEPOffset(&Builder, *TD, &GEP);
Value *Offset = EmitGEPOffset(&Builder, *TD, &GEP, /*NoAssumptions=*/true);
Offset = Builder.CreateAdd(PtrData.second, Offset);
return std::make_pair(PtrData.first, Offset);
}

10
test/Instrumentation/BoundsChecking/simple.ll
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@ -116,3 +116,13 @@ define void @f11(i128* byval %x) nounwind {
%3 = load i8* %2, align 4
ret void
}
; CHECK: @f12
define i64 @f12(i64 %x, i64 %y) nounwind {
%1 = tail call i8* @calloc(i64 1, i64 %x)
; CHECK: mul i64 %y, 8
%2 = bitcast i8* %1 to i64*
%3 = getelementptr inbounds i64* %2, i64 %y
%4 = load i64* %3, align 8
ret i64 %4
}